(1) Development of procedures for the electrophoretic separation of large (greater than 10 to the 8th power dalton) DNA molecules will be continued, employing bacteria virus G DNA (5 x 10 to the 8th power daltons) as a standard. (2) Naturally occurring cross-links which we have found in yeast chromosomal DNA will be further examined to determine whether they occur at specific sites, if and when in the cell cycle they are removed and regenerated, and their chemical nature. (3) Experiments employing protein density label will be carried out to examine the pattern of segregation or exchange of nucleosomal histones in yeast. (4) The molecular basis of variation in the length of the yeast S period will be examined. (5) Experiments will be begun to develop procedures for the determination of the specificity and regulation of replication initiation sites in yeast chromosomes. BIBLIOGRAPHIC REFERENCES: Forte, M.A. and W.L. Fangman. (1976). Naturally occurring cross-links in yeast chromosomal DNA. Cell 8, 425-431. Burke, W. and W.L. Fangman. (1975). Temporal order in yeast chromosome replication. Cell 5, 263-269.